JPH1117071A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the warp of a molded product and minimize the internal stress due to mounting on a heat sink to realize a high reliability and ensure a low thermal resistance, by specifying the linear expansion coefficient ratio of a metal board to a resin mold. SOLUTION: A device has a power semiconductor element 11 fixed to a lead frame 13 through a solder layer. The lead frame 13 is adhered to a metal board 19 through an insulation layer 18, the element 11 is electrically bonded by an Al wire bonding part 16 and molded with an armor resin mold 17 to form an integrated structure, and the linear thermal expansion coefficient of the resin mold 17 is adjusted relative to that of the board 11 in a ratio of 0.3:1-0.6:1 in the actual temp. range. Thus, the warp of the molded product is suppressed, and hence the internal stress due to mounting on a heat sink, etc., is minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a chip component including a semiconductor element mounted on a metal substrate via an insulating layer,
The present invention relates to a resin-encapsulated semiconductor device having a structure entirely protected by an exterior mold, and in particular, to prevent warpage caused by a difference in linear expansion coefficient between main structural materials constituting the semiconductor device, such as a metal substrate and a mold resin. The present invention relates to a power semiconductor device that achieves high reliability by taking measures for performing such operations. Therefore, the semiconductor device according to the present invention can be effectively used as an output control inverter for general-purpose and industrial equipment.

[0002]

2. Description of the Related Art As a conventional power semiconductor device of this type,
There is a configuration disclosed in Japanese Patent Publication No. 7-249714.
This is one in which a conductive circuit is formed on an Al substrate, a power semiconductor element is mounted thereon, and the exterior is molded using a resin having a linear expansion coefficient smaller than that of the Al substrate. In a semiconductor device having this structure, a plurality of power semiconductor elements and other components are often mounted together, resulting in an increase in substrate size. When the substrate size is large, even if there is a slight warpage, it is emphasized, so that it is difficult to realize sufficient flatness after molding of the semiconductor device, and it is also difficult to secure reliability. There is.

[0003]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the conventional method and realizes a highly reliable power semiconductor device having good flatness. That is, the warpage of the semiconductor device is mainly determined by the balance between the coefficient of linear expansion of the metal substrate constituting the semiconductor device and the mold resin. However, there is a large difference in the temperature dependence of the coefficient of linear expansion between the two.
By optimizing the combination of the two in consideration of the temperature dependence, even if the semiconductor device has a large substrate size, the amount of warpage can be minimized, and as a result, a highly reliable power semiconductor device can be obtained. I will provide a.

[0004]

In order to achieve the above object, the present invention takes the following measures.

[0005] 1. A conductor circuit is formed on one surface of a metal substrate via an insulating layer, a plurality of heat-generating semiconductor elements are fixed on the conductor circuit, and at least a part of another surface of the metal substrate is substantially exposed to the outside. In the semiconductor device having a composite structure protected by the integral electric insulating exterior resin mold in this state, the ratio of the coefficient of linear expansion in the practical temperature range is such that the ratio of the resin mold to the metal substrate 1.0 is zero. .3
To 0.6.

[0006] 2. In the above item 1, the metal substrate may be made of Al
Alternatively, it is made of an Al alloy, has a linear expansion coefficient in a practical temperature range of 21 ppm / ° C. to 25 ppm / ° C., and has a linear expansion coefficient of 8 ppm / ° C. to 14 ppm /
The semiconductor device is configured so as to be adjusted to the range of ° C.

[0007] 3. In the above item 1, the metal substrate may be made of Cu
Alternatively, the resin mold has a linear expansion coefficient of 17 ppm / ° C. to 21 ppm / ° C. in a practical temperature range, and a linear expansion coefficient of 6 ppm / ° C. to 12 ppm /
The semiconductor device is configured so as to be adjusted to the range of ° C.

As shown in the sectional structure of FIG. 1, the warpage of this type of resin-encapsulated semiconductor device is determined by the balance between the linear expansion coefficients of the metal substrate having the highest volume occupancy and the resin. However, there is a great difference in the temperature dependence of the linear expansion between the two, and special consideration in the manufacturing process is required to ensure flatness. FIG. 2 shows the relationship between the linear expansion of the Al substrate and the temperature. Here, the linear expansion coefficient α is represented by the ratio between the linear expansion and the temperature change, that is, the gradient of the straight line shown in FIG. FIG. 3 shows the relationship between the amount of shrinkage and the temperature during molding of a typical epoxy resin material for transfer molding. The mark x in the figure is the solidification starting point, which can be roughly classified into three regions according to the temperature, and is defined as follows. A: Chemical shrinkage area-an area where the liquid resin starts to crosslink and solidifies. B: pre-heat shrinkage area-glass transition temperature (Tg)
The contraction rate of this region is α2. C: Late heat shrinkage region—a heat shrinkage region at a temperature lower than Tg, and the shrinkage ratio during that period is α1. Normal α1
The ratio between α1 and α2 is 1/3 and α1 is small. The apparent shrinkage at the time of resin molding is obtained by summing up these. The apparent contraction rate A is obtained as the gradient of the broken line A in FIG. 3, and includes the total contraction amount from the liquid state. The apparent shrinkage ratio B is a gradient of a broken line B and represents an average shrinkage amount from the end of solidification to room temperature.

[0009] After the molding, post-curing for further curing the resin tends to further reduce the shrinkage. Usually, the shrinkage rate α1 in this state is simply referred to as the linear expansion rate or shrinkage rate of the resin, and is herein referred to as the steady shrinkage rate to distinguish it from the above-described shrinkage rate.

If a metal substrate and a resin having a constant contraction rate equal to the coefficient of linear expansion of the substrate are combined and formed into a shape shown in FIG. 1, a convex warpage occurs on the metal substrate surface side.
Sufficient flatness cannot be obtained. This is considered to be the result of the apparent shrinkage of the resin being extremely large compared to the metal substrate. The present inventors have found the following conditions necessary for ensuring flatness as a result of repeated experiments. That is, even if the linear expansion coefficient α of the applied metal substrate is high, the apparent contraction rate A of the resin is high, and the apparent contraction rate B is low if the linear expansion coefficient α is low.
Is set in the range. This is expressed as a steady-state contraction rate based on an experimental rule as follows. That is, by setting the steady shrinkage of the resin in the range of 0.3 to 0.5 with respect to the linear expansion coefficient of the metal substrate of 1.0, the condition of the apparent shrinkage can be almost satisfied. By a combination of materials meeting the conditions, a molded article having sufficient flatness after molding can be obtained.

Generally, there is a strong correlation between the steady shrinkage of the resin, which is simply referred to as the shrinkage, and the apparent shrinkage. The reason is as follows. This kind of resin material adjusts the characteristics of the material by adding a filler such as alumina or silica having a low coefficient of thermal expansion to a resin having a very high coefficient of linear expansion such as an epoxy resin. Accordingly, the coefficient of linear expansion greatly varies depending on the blending ratio of the two, and as described above, the coefficient of linear expansion decreases as the ratio of the filler increases. The situation where the coefficient of linear expansion is determined by the ratio of the filler is a phenomenon common to each of the regions A, B and C in FIG. 3, and the steady-state shrinkage and the apparent shrinkage tend to be almost directly proportional.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Embodiment 1 FIG. 1 is a sectional view of a semiconductor device according to an embodiment of the present invention. For example, IGBT (Insulated Gate Bipolar Transis
A power semiconductor element 11 such as tor) is fixed on the lead frame 13 via the solder layer 12. The lead frame 13 is bonded to a metal substrate 19 via an insulating layer 18,
The element 11 has a structure in which it is electrically connected by an aluminum wire bonding portion 16 and the whole system is integrally molded by an exterior resin mold 17. Metal substrate 19 has a purity of 9
An 9.9% Al plate having dimensions of 70 mm × 40 mm × 2 mm was used. The coefficient of linear expansion of this substrate is 23.5 ppm / ° C. As the resin material, a linear expansion coefficient was adjusted by adding an appropriate amount of silica powder to an epoxy resin. Table 1 shows the measurement results of the shrinkage rates of these resin materials. In the measurement, the temperature change of the length of the cylindrical sample set in the mold was directly measured via a displacement detection rod.

The metal substrate 19 on which the element 11 and the lead frame 13 were mounted was set in a mold, and was molded at 180 ° C. by a transfer molding method. The molding dimension in FIG. 1 was 1 mm and the dimension t was 6 mm. After molding, post-curing is further performed for 5 hours at 180 ° C.
9 was evaluated for the amount of warpage of the exposed surface. In the evaluation, the displacement of the surface was measured continuously on a diagonal line, and the largest value was defined as the amount of warpage. Displacement convex on the metal substrate side is expressed as positive, and conversely, convex on the resin side is expressed as negative warpage.

[0015] Negative warpage is not preferable because a gap is formed between the semiconductor device and the heat radiating member, and the thermal resistance increases. On the other hand, if the positive warpage is large, the internal stress increases when attaching to the heat dissipation member, and sufficient reliability cannot be obtained.
The range of warpage is practically preferably in the range of −20 μm to +80 μm. From the results shown in Table 1, it can be seen that the preferable steady-state shrinkage rate in this example is in the range of 8.4 ppm / ° C to 11.5 ppm / ° C.

[0016]

[Table 1]

Example 2 As a metal substrate 19, a Cu plate having a purity of 99.5% was used.
Otherwise, including the dimensions of the substrate, a sample was prepared in the same manner as in Example 1, and the warpage of the substrate surface was measured in the same manner. The coefficient of linear expansion of the metal substrate 19 is 17.7 ppm / ° C.
It is.

Table 2 shows the measurement results. From this, it can be seen that when a Cu-based substrate is applied, the preferable range of the mold resin 17 is 6.8 ppm / ° C. to 8.4 ppm / ° C. Example 3 A sample was prepared in the same manner as in Example 1, and the warpage of the substrate surface was measured in the same manner. Here, attention was paid to the dimensions of the metal substrate 19, and the relationship with the warpage was evaluated. FIG. 4 shows the measurement results. The amount of warpage increases as the substrate size increases.
For this reason, the preferable range of the warpage is from −20 μm to +80.
It is shown that the linear expansion coefficient of the resin 17 needs to be set in a narrower range as the size of the substrate is larger, and conversely, the applicable range of the linear expansion coefficient of the applicable resin is wider with a smaller substrate.

Example 4 A sample was prepared in the same manner as in Example 1, and the warpage of the substrate surface was measured in the same manner. Here, the thickness of the molded body, t
Focusing on dimensions, the relationship with warpage was evaluated. FIG. 5 shows the measurement results. The amount of warpage tends to increase slightly as the t dimension increases.

Example 5 By the same procedure as in Example 1, a converter and inverter composite power semiconductor device having the circuit pattern shown in FIG. 6 was manufactured. This device was directly attached to a three-phase induction motor to integrate them. FIG. 7 shows a block diagram of the electric circuit. Since the semiconductor device according to the present invention has a small warpage of the substrate, low thermal resistance and high reliability, it can be integrated with a motor used in a severe environment, for example, an electric vehicle, various pumps, and a motor for transportation. It becomes possible. By integrating the inverter and the motor in this way, it is possible to realize the miniaturization and high reliability of each device as a whole.

[0021]

As described above, according to the present invention,
By specifying the linear expansion coefficient ratio between the metal substrate 19 and the resin mold 17, the warpage of the molded body after molding can be controlled, so that the internal stress due to attachment to the heat radiating member is minimized, and high reliability is achieved. And the effect of ensuring low thermal resistance.

[Brief description of the drawings]

FIG. 1 is a sectional configuration diagram of a power semiconductor device according to an embodiment of the present invention.

FIG. 2 shows the linear expansion temperature dependence of a metal substrate.

FIG. 3 shows the linear expansion temperature dependency of a mold resin.

FIG. 4 shows the relationship between the amount of warpage of a molded article and the dimensions of a substrate.

FIG. 5 shows the relationship between the amount of warpage of a molded article and the thickness of the molded article.

FIG. 6 is a circuit pattern diagram of an inverter module according to an embodiment of the present invention.

FIG. 7 is a circuit block diagram of an inverter device according to one embodiment of the present invention.

[Explanation of symbols]

11 semiconductor element, 11a rectifier diode, 11b
IGBT, 11c ... freewheel diode, 12 ...
Solder, 13: Lead frame, 13a: Main circuit terminal,
13b: Control system terminal, 16: Wire bonding part, 17
... exterior resin mold, 19 ... metal substrate, 25 ... thermistor, 26 ... shunt resistor, 31 ... converter part, 32 ...
Inverter part, 33 ... heat radiation part.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Noritaka Kamimura 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd. (72) Kazuhiro Suzuki 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 Inside the Hitachi Research Laboratory, Hitachi, Ltd.

Claims (3)

[Claims] 1. A conductive circuit is formed on one surface of a metal substrate via an insulating layer, a plurality of heat-generating semiconductor elements are fixed on the conductive circuit, and at least a part of another surface of the metal substrate is substantially formed. In a semiconductor device having a composite structure, which is protected by an integral electrically insulating exterior resin mold while being exposed to the outside, the ratio of the coefficient of linear expansion in a practical temperature range is higher than that of the metal substrate 1.0. A semiconductor device, wherein the resin mold is configured to be adjusted in a range of 0.3 to 0.6. 2. The resin substrate according to claim 1, wherein said metal substrate is made of Al or an Al alloy, has a linear expansion coefficient in a practical temperature range of 21 ppm / ° C. to 25 ppm / ° C., and has a linear expansion coefficient of said resin mold. 8ppm / ℃ to 14ppm / ℃
A semiconductor device characterized in that the semiconductor device is configured to be adjusted in the range of: 3. The method according to claim 1, wherein the metal substrate is made of Cu or a Cu alloy, has a linear expansion coefficient in a practical temperature range of 17 ppm / ° C. to 21 ppm / ° C., and has a linear expansion coefficient of the resin mold. 6ppm / ℃ to 12ppm / ℃
A semiconductor device characterized in that the semiconductor device is configured to be adjusted in the range of: